1. Field of the Technology
The present invention relates generally to Code Division Multiple Access (CDMA) cellular mobile communication system, and more particularly to a smart antenna technology applied in a Frequency Division Duplex (FDD) CDMA cellular mobile communication system.
2. Description of Related Art
Smart antenna technology is one of the most important technologies in modem wireless communications. Especially, when smart antenna technology is used in a CDMA cellular mobile communication system, there are advantages, such as greatly increasing system capacity, increasing the cover range of a wireless base station, decreasing system cost and raising system performance, etc. Therefore, smart antenna technology has become an important technology concern all over the world.
At present, smart antenna technology is mainly used in time division duplex (TDD) CDMA wireless communication systems including cellular mobile communication systems, wireless subscriber loops and wireless local area networks, etc. The main reason is that in a TDD system, a transmitting channel and a receiving channel use the same frequencies and the electric-wave propagation characteristics of uplink (receiving) and downlink (transmitting) are the same. Therefore, parameters of receiving signal beam forming obtained from the uplink can be again used for downlink beam forming. Consequently, the advantages of smart antenna technologies are brought into full play.
Nevertheless, in present cellular mobile communication systems, an FDD wireless communication system is the most popular one. In a FDD wireless communication system, uplink and downlink use different carrier frequencies and the electric-wave propagation characteristics of uplink and downlink are totally different. The result is that the parameters of receiving signal beam forming obtained from the uplink cannot be again used for downlink beam forming, so the advantages of smart antenna technology cannot be brought into full play.
In a base station of a FDD wireless communication system, when using smart antennas the receiving link and the transmitting link work simultaneously with different frequency bands, so one set or multiple sets of smart antenna arrays can be used for receiving and transmitting, respectively. A working method and principle of the receiving link smart antenna using smart antenna technology in a TDD wireless communication system can be referenced in Chinese Patent ZL 97 1 04039.7 titled: “A Time Division Duplex Synchronous CDMA Wireless Communication System With Smart Antenna.” However, the beam forming of the transmitting downlink cannot simply use the parameters obtained from the receiving uplink beam forming associated with every antenna unit. This is determined by unsymmetrical electric-wave propagation characteristics of uplink and downlink in a FDD wireless communication system.